Neural organization and neural interactions in mammalian retinas are investigated using intracellular electrophysiology, electron microscopy, and pharmacology. A flat mount, superfused retina preparation has been devised for the cat. In this preparation, electrodes are aimed under visual control at retinal neurons, and penetration is verified by immediate staining of the impaled cell. Intracellular recordings from retinal ganglion cells with 50 mV resting potentials, 40 mV action potentials, and 10 mV light-induced generator potentials could be maintained in excess of one hour. Space constants of horizontal cells (HC's) in rabbit and cat retinas were calculated from the amplitude of responses to a 200 microM-wide light bar presented at different positions across the receptive field. Dopaminergic drugs (35-750 microM) were administered through the perfusion media. Apomorphine consistently increased rabbit HC space constants (20-150%). Five other ligands including the D/1 specific agonist SKF38393, the D/1 antagonist SCH23390, the D/2 agonist quinpirole, the D/2 antagonist sulpiride, and dopamine itself induced only small (<25%), inconsistent changes in space constant. Apomorphine effects were evident in rabbit, but not cat. Dopaminergic ligands affect HC space constants, but may not follow classic patterns of D/1-D/2 agonism and antagonism. ON-OFF amacrine cells in cat retina were studied electrophysiologically and stained with HRP for morphological and ultrastructural investigation. Stained cells were of three types: A19, A20 and A22. The types varied in level of branching in the inner plexiform layer, and in synaptic connectivity. Arborizations were monostratified and consisted of two zones: a central zone of dendritic branching, and a more distal zone of multiple axon-like processes. Gaussian receptive field radii ( 566 +/- 100 microM) were larger than central dendritic zone diameters, reflecting signals from an area covered by the long axon-like processes. Predominantly rod signals were seen at ON, whereas evenly mixed rod and cone signals were seen at OFF. Reversal potentials for both ON and OFF components were 25-35 mV, associated with conductance increases from 0.1- 0.4 nS.